[25: Special Eurobarometer 338 (April 2010), Special Eurobarometer 407 (November 2013) and Special Eurobarometer 445 (June 2016)]
[25: Speciale Eurobarometer 338 (april 2010), Speciale Eurobarometer 407 (november 2013) en Speciale Eurobarometer 445 (juni 2016).]